In electromagnetism, the concept of Poynting vector as measured by an observer is well known. A mathematical analogue in general relativity is the super-Poynting vector of the Weyl tensor. Observers for which the (super-)Poynting vector vanishes are called principal. When, at a given point, the electromagnetic field is non-null, or the gravitational field is of Weyl–Petrov type I or D, principal observers instantaneously passing through that point always exist. We survey characterizations of such observers and study their relation to arbitrary observers. In the non-null electromagnetic case it is known that, given any observer, there is a principal observer which moves relative to the first in the direction of his Poynting vector. Replacing Poynting by super-Poynting yields a possible gravitational analogue; we show that this analogy indeed holds for any observer when the Petrov type is D, but only for a one-dimensional variety of observers when the Petrov type is I. We provide algorithms to obtain the principal observers directly from the electric and magnetic fields (in the electromagnetic case) or electric and magnetic parts of the Weyl tensor (in the gravitational case) relative to an arbitrary observer. It is found that in Petrov type D doubly aligned non-null Einstein–Maxwell fields (which include all classical charged black hole solutions) the Poynting and super-Poynting vectors are aligned, at each point and for each observer, and the principal observers coincide. Our results are illustrated in simple examples.

在电磁学中，观察者测量的坡印廷矢量的概念是众所周知的。广义相对论中的一个数学类比是外尔张量的超坡印廷向量。（超）坡印廷向量消失的观察者被称为主体. 当在给定的点上，电磁场是非零的，或者引力场是 Weyl-Petrov I 型或 D 型时，瞬时通过该点的主要观察者总是存在的。我们调查了这些观察者的特征并研究了他们与任意观察者的关系。在非零电磁情况下，已知给定任何观察者，都有一个主要观察者在其坡印廷矢量的方向上相对于第一个观察者移动。用超级坡印亭代替坡印亭会产生一个可能的引力类似物；我们证明，当 Petrov 类型为 D 时，这个类比确实适用于任何观察者，但仅适用于 Petrov 类型为 I 时的一维观察者。我们提供的算法可以直接从相对于任意观察者的电场和磁场（在电磁情况下）或外尔张量的电和磁部分（在引力情况下）获得主要观察者。发现在彼得罗夫 D 型双对齐非零爱因斯坦-麦克斯韦场（包括所有经典带电黑洞解）中，坡印廷和超坡印廷矢量在每个点和每个观察者处对齐，并且主观察者重合. 我们的结果用简单的例子来说明。在每个点和每个观察者，和主要观察者重合。我们的结果用简单的例子来说明。在每个点和每个观察者，和主要观察者重合。我们的结果用简单的例子来说明。